The general aim of this project is to describe mechanisms by which the membrane electrical properties of excitable cells can be modulated by events occurring within the intracellular environment, both during ontogeny and in adult cells. It is clear that the properties of voltage-dependent ion channels are not invariant and that changes occur in ways designed to intergrate the electrical properties of the cell into its overall biological functioning. Understanding how this occurs is relevant to problems of the developmental of excitable cells and plasticity in adult neurons. Few preparations exist in which it is possible to carry out a detailed analysis of the events underlying physiologically important changes in the active electrical properties of the membrane. It has been known for several years that the oocytes of many marine invertebrates are electrically excitable and possess voltage-gated ion channels similar to those found in adult nerve and muscle. Futhermore, it has been demonstrated in several instances that the properties of these ion channels change during various states of early development before first cleavage, particularly during maturation (the reinitiation of meiosis prior to fertilization) and fertilization. It is known that the changes in ion channel properties during maturation play a crucial physiological role in preparing the egg for fertilization but virtually nothing is known about the mechanisms which these changes occur. In this proposal I will use starfish oocytes, which are amenable to a variety of electrophysiological techniques, to study the problem of ion channel modulation. I will investigate changes in the properties of voltage-dependent ion currents which occur during maturation and fertilization of the oocytes in vitro. The goal of the experiments is to understand the mechanisms by which ion channel properties are altered during early stages of development.